Heat exchanger



June 22, 1943. E, A. DEWALD HEAT EXCHANGER Filed Dec. 23, 1939 Patented June 22, 1943 2,322,284 HEAT EXCHANGER Edward A. Dewald, Massillon, Ohio, assignor to The Griscom-Russell Company, New York, N. Y., a corporation of Delaware Application December 23, 1939, Serial No. 310,689

6 Claims.

This invention relates to flow retarders particularly for use in heat exchangers and to the combination of such retarders with finned-tube heat exchangers.

Flow retarders found in the prior art, as I am to a very marked degree by an unretarded flow.'

It has, therefore, been customary instead of employinga retarder in heat exchangers to use finned tubing, either helical or longitudinal, to improve the heat transfer rate in heat exchangers. Neither of these expedients is wholly satisfactory, since the helical type fin results in a very considerable pressure drop due to fluid resistance and the longitudinal type fin does not wholly destroy the cold core" of the flow past it.

An object of my invention, therefore, is to provide in a heat exchanger an efiicient sheetmetal flow retarder particularly adapted for use with longitudinal finned tubing. It is a further object of this invention to provide such a. retarder which will be inexpensive to-manufacture,

easy to assemble and disassemble, and, therefore,

easy to clean. Still another object is to provide a flow retarder which will be easy to adapt to existing finned exchan ers or to exchangers newly manufactured to existing designs.

I have accomplished this object in a simple preferred embodiment of my retarder by slitting a strip of sheet metal on its central longitudinal axis at regularly spaced intervals and by spreading slightly the sheet metal above and below each slit to give a double-wave form to the retarder seen in plan.

For a fuller understanding of the invention, reference may be had to the accompanying drawing, in which: 7 Fig. 1 is an elevatio of a retarder constructed according to my invention;

Fig. 2 is a plan view of the same; Fig. 3 is a section taken on the line 3-3 of Fig. 2;

Fig. 4 is a section taken on the line 4-4 01' E18.

Fig. 5 is an elevation, partly in section on the line 55 of Fig. 6, of a longitudinally finned heat exchanger employing a retarder of my invention;

and

Fi 6 is a section taken on the line 6-6 of Fig. 5.

In the drawing, Figs. 1 through 4 show a preferred construction of the retarder proper and Figs. 5 and 6 a finned-tube heat exchanger provided with retarders. The retarder I, is constructed from a strip of sheet metal slit centrally at regularly spaced intervals, the slits 2 being considerably greater than the uncut portions 3. After slitting, the upper portions 4 above the slits 2 are pressed out alternately to the right and left of the axis of the metal strip giving to the upper half of the strip a substantially-continuous, gentle wave-form in plan, the nodes of the Waves being the uncut portions 3 of the metal strip. The lower portions ibelow the slits 2 are likewise alternately pressed out to the right and left, but opposite to the position of the upper portions 4. The plan of the lower portion of the retarder is, therefore, likewise a gentle wave-form with its nodes at the uncut portions 3, but the crests of the wave-form of the lower portions 5 are opposite to the crests of the waveform of the upper portions 4.

. The structure of this retarder is thus admirably suited to its purpose. The double wave form of the retarder gives a considerable desirable turbulence to the flow past it which fully destroys any core effect and substantially prevents the formation of an insulating gaslayer on the heat transfer surfaces of the exchanger in which it is employed, while the gentle waveform of its protuberances does not cause a marked pressure drop due to fluid resistance. Expressed in other terms, the flow retarder of my invention is "streamlined" producing a controlled turbulence without excessive fluid friction.

While I have described in detail,'as a preferred embodiment of my invention a simple, efiective and inexpensive form of retarder, it will be readily apparent that a number of variations from the specific shape illustrated may be made without departing from the spirit thereof. For example, an additional row or rows of slits may be employed to give a triple or multiple waveform to the retarder. Or the retarder may be built up of separate Strips of sheet material for each wave form welded or fastened together at the nodal points.

As shown in Figs. 1 and 2, the metal above the slits 2 at the ends of the retarder strip I is cut away leaving the notches or recesses 6. When employed in the embodiment of my invention shown in Figs. 5 and 6, these notches 6 are employed as seats for the' split retaining rings 1 which hold the retarder strips I in place between the longitudinal fins 8 of the heat exchanger 9. The heat exchanger 9, shown in Figs. 5 and 6, is of the spur tube type and may be employed to transfer heat from a heating medium entering the shell l4 through the inlet l and passing out through the outlet II to fluid entering inlet l2 and passing through the finned pipe IS in annular flow around the inner pipe IE to the return chamber l1 and thence back through the inner pipe l6 and out the outlet l3. The fins B on the pipe l5, as the heat exchanger is ordinarily constructed, serve with a fair degree of efficiency to insure a rapid rate of heat exchange between the heating and heated fluids.

By combination with a retarder according to my invention, however, the rate of heat transfer is increased to a marked degree with only a slight and by no means corresponding loss due to the pressure drop caused by added hydraulic resistance. In the embodiment illustrated a retarder l of the form shown in Figs. 1-4 is inserted parallel to and between each of the fins 8, as shown in section in Fig. 6.

It will be observed that the cleaning of the finned Jexchanger shown in Figs. and 6 is not made more difficult by the employment of the retarder of my invention, since, when the finned tube I5 is withdrawn from the shell M as before, th retarder bundle is brought out with that tube by the split retaining rings '1. so removed, the finned tube l5 may be separated from the bundle of retarders l by taking off either of the split retainer rings 1.

Thus, I have provided by my invention a flow retarder of a novel and particularly efiicient construction which may be applied both to new and old exchangers and which is especially adapted for a novel combination with finned heat exchangers, the use of fins and retarders having heretofore been regarded as substitutes and mutually exclusive.

While I have illustrated and described my invention in terms of a retarder designed for specific application to the heat exchanger shown, it

will be apparent to those skilled in the art that f a number of changes may be made without departing from the spirit and scope of my invention. For example, other retaining means than the split ring and notch illustrated might be employed, and the precise contours of the wave forms illustrated may necessarily be varied from application to application depending upon the dimensions of the particular exchanger, the spacing of the fins or the velocity of the flow which they are intended to retard.

I claim:

1. A flow retarder comprising a strip of sheet material having successive longitudinal slits along a line substantially coincident with its lengitudinal axis and uncut portions between said slits, the material on the opposite sides of each of said slits being bent oppositely outward and the material on the same side of successive slits being also bent oppositely outward the maximum displacement of the bent portions from the plane of the strip being slight compared with the When once length of the slits and, the shape of the bends thus formed being a entle wave.

2. A flow retarder comprising a strip of sheet material having a row of successive central longitudinal slits along a line substantially coincident with its longitudinal axis and uncut portions between said slits, the material on the opposite sides of each of said slits being bent oppositely outward and the material on the same side of successive slits being also bent oppositely outward the maximum displacement of the bent portions from the plane of the strip being slight compared with the length of the slits and the shape of the bends thus formed being a gentle wave.

3. An exchanger for transferring heat between fluids in two or more closed circuits comprising one or more longitudinally-finned tube heattransfer elements and fiow retarders of sheet material interposed between the fins of said elements, said retarders'comprising a stripof sheet material having successive longitudinal slits therein and uncut portions between said slits, the material on the opposite sides of each of said slits being bent oppositely outward and the material.

on the same side of successive slits being also bent oppositely outward.

4. An exchanger for transferring heat between fluids in two or more closed circuits comprising one or more longitudinally-finned tube heattransfer elements and flow retarders of sheet material interposed between the fins of said elements, said retarders comprising a strip of sheet material having a row of successive central longitudinal slits therein and uncut portions between said slits, the material on the opposite sides of each of said slits being bent oppositely outward and the material on the same side of successive slits being also bent oppositely outward, the shape of the bends thus formed being a gentle'wave.

5. An exchanger for transferring heat between fluids in two or more closed circuits comprising one or more longitudinally-finned tube heattransfer elements and flow retarders of sheet material interposed between the fins of said elements, said retarders comprising a strip of sheet material having a row of central longitudinal,

slits therein and uncut portions between said slits, the material on the opposite sides of each of said slits being bent oppositely outward and the material on the same side of successive slits being also bent oppositely outward, said retarders being removably afiixed to said finned elements so as to be a unit therewith when said elements are assembled and disassembled in the complete exchanger.

6. An exchanger for transferring heat between fluids in two or more closed circuits comprising one or more tubular heat-transfer elements having fins afiixed longitudinally thereon centrally for a substantial portion of the length thereof, flow retarders of sheet material interposed between and longer than said fins, said retarders having three sided notches on the upper side of the ends thereof and removable retaining rings fitted into said notches beyond the ends of said fins, whereby said retarders are maintained in position around said tubular elements. and between the fins thereof both laterally and longitudinally.

EDWARD A. DEWALD. 

